Data storage devices commonly have a recording head that includes a read transducer that reads information from a data storage medium and a write transducer that writes information to a data storage medium.
In magnetic data storage devices such as disc drives, a magnetoresistive (MR) sensor such as a Giant Magnetoresistive (GMR) sensor or a Tunnel Junction Magnetoresistive (TMR) sensor may be employed as the read transducer to read a magnetic signal from the magnetic media. The MR sensor has an electrical resistance that changes in response to an external magnetic field. This change in electrical resistance can be detected by processing circuitry in order to read magnetic data from the adjacent magnetic media.
With ever-increasing levels of recording density in disc drives and a need for faster data transfer speeds, the read transducer needs to have correspondingly better data-reproducing capabilities. A multiple-sensor read device may be of choice of sensor for high areal density, high signal-to-noise ratio in the hard-disk drive based storage system.
To provide multiple read transducer elements, the multiple readers can be stacked to one another within the multilayer portion and topography from the lower structures should be minimized in order to prevent degradation of performance of reader stacked on top. In other words, the planarization of the lower reader in a stacked multiple sensor device is important for the performance of an upper reader stacked on top of the lower reader.
In the process of making functional reader devices, there can be a need to pattern a sheet film of the multilayer thin film portion either with a photoresist or by a hard mask to facilitate the removal of a partial or the entire thick ness of one or more film portions that are not covered by the photo-resist or mask. The removal process typically comprises an ion milling process that is controlled based upon the level of film layer removal that is required to create a desired thin film structure. After the milling process is complete, the structure of the thin film may then be backfilled with another material or structure as part of a functional device. Then, the photo-resist or mask is stripped or lifted off from the etched film layer, leaving the structured thin film layer backfilled with other material, the combination structure of which can be utilized in functional device fabrication. For example, in creating read elements, a thin film metal layer can be deposited over the backfilled combination structure.
Specifically, in the case of milling a structure within a layer utilizing a mask or photo-resist material followed by backfilling with other material, surface topographical effects can be seen, especially with devices in the nanometer size range. Topography can form as a result of shadow effects of the photo-resist or hard mask to a milling process. Or, topography can form as a result of the deposition of the backfilled material. The area of the juncture of the structured layer and the backfilled material is an area where topography, such as an outward bump can form. With nano-sized devices, bumps, recesses and other surface features can form that are typically within the range of 10-100 nanometers. This topography will then propagate to a further layer or structure that is deposited over the backfilled structure, which can affect the functionality of the fabricated device, such as in a multiple sensor read device.
In order to reduce any created topography, such as at the junction of the backfilled material with the structured layer, chemical-mechanical polishing (CMP) is known as a process for surface planarization. CMP can be successfully utilized to achieve planarization at the materials junction. However, it has be observed that other adjacent material zones, like the backfilled material within the structure, can dish inward as a result of the degree of CMP required at the junction.
Also, a CMP process utilizes a slurry that comprises abrasive particles within wet chemicals. It has also been observed that the wet chemical can invade the interface between the structured layer and the backfilled material causing a deleterious effect. Specifically, the wet chemical can etch or corrode the materials at the material interfaces.